For years, chocolate lovers have remained blissfully unaware of the precise reason bittersweet dark chocolate seems to improve cardiovascular health. At least until, now that is.

On Tuesday, researchers at meeting of the American Chemical Society (ACS) in Dallas said they had solved the confection conundrum: Specific chocolate-loving microbes in the gut convert an otherwise indigestible portion of the candy into anti-inflammatory compounds, they said.

Using a series of modified test tubes to simulate humans' gurgling guts, researchers exposed several forms of cocoa powder to digestive juices and enzymes, and then to bacteria found in samples of human feces.

What they found was that after cocoa was "digested," long molecules called polyphenolic polymers remained within the gastrointestinal, or GI, tract.

The molecules are too large to cross the walls of the gut and be used as nutrients, according to researcher John Finley, a professor of food science and biochemistry at Louisiana State University.

"They do nothing for us except travel down the GI tract after we consume them," Finley said.

That is until they encounter some of the many microbes that inhabit the human colon, particularly Bifidobacterium and lactic acid bacteria, researchers said.

"These little guys say, 'Hey — there's something in there that I can use,' and they start to break it down," Finley said.

The smaller molecules that result from this fermentation can travel through the gut wall and be used by the body, researchers said.

"These materials are anti-inflammatory and they serve to prevent or delay the onset of some forms of cardiovascular disease that are associated with inflammation," Finley said.

A number of short-term studies conducted in recent years have suggested that dark chocolate can cause blood vessels to dilate, and thus lower blood pressure, although this is not the case with white chocolate and milk chocolate.

It has been unclear exactly why this happens, but researchers had focused on the effects of anti-oxidant flavanols, such as catechin and epicatechin.

Finley said these were among the compounds that were poorly digested, yet acted upon by gut microbes. The other substance that was fermented was dietary fiber, which makes up about 30% of cocoa powder.

He said that the amount of cocoa powder that appeared to produce beneficial effects was about two tablespoons a day.

One of the issues involving dark chocolate, Finley said, was the amount of sugar and fat that chocolate candy contained. He said you could avoid those substances by putting cocoa powder on oatmeal, as he does.

He said it was possible that the beneficial compounds contained within cocoa powder might one day be processed into pill form, and noted that Mars Inc., the maker of M&M candy, was partially funding research into that possibility.

Finely said he wasn't very excited by this prospect.

"I would rather eat a big old chocolate cookie or a cup of cocoa than ... take a pill," he said.

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